This invention concerns a method and a device for assembling several components and particularly connection fittings for fluid couplings.
Couplings are known in the prior art into which components made of a hard material (such as metal, or plastics reinforced with very hard glass fibers) are force fitted, for example with retaining ribs, into bodies of a softer material, especially plastic.
By this method, the material remains stressed and often, after a long time, breaks in an unacceptable and hazardous manner.
Another prior art method consists of fitting hard components, in particular metal inserts, into parts of a softer material with the help of ultrasonics. Unfortunately, this approach cannot be utilized when the inserted bodies are too large or when the components are too long.
Furthermore, the latter method does not always eliminate internal stresses in the softer substance of the body and the risks of rupturing in the long run, ie. after one to five years, remains high, something which is unacceptable in terms of safety for fluid couplings.
There are still other methods of fitting inserts, especially metallic inserts, into a part by which capture in the supporting part is accomplished either by expansion of the insert after insertion or by elasticity, as in the case of split inserts, or otherwise by self-tapping,as in the case where an insert effectively "machines" its capture means by rotation. All of these methods share a common drawback stemming from the fact that considerable tension must be maintained between the parts after they have been fit together, which might cause breaks in the long run.
Still another known method consists of inserting parts by remolding them into other parts at the time of injection. However, this is a costly process, because the inserts must be manually placed inside the mold, and accordingly penalizes throughput.
The present inventors had attempted to overcome this problem by utilizing a device which was the subject of French Pat. No. 2,399,608 in which a ribbed end fitting is force fitted into a body made of a softer material in such a manner that the relatively slow rotation of the rib drives a groove in the softer body. However, this method has not proved satisfactory due to the difficulty of making such a rib in the hard material, for example metal.
Still another known method involves the friction welding of two parts by pressing them together as they are rotated and thus heating them until local melting bonds them together. But this works only with identical materials, whether hard or soft, never with two materials having different hardnesses, as required for the present invention.